This is more like "players' hell" than "GM hell", but ....
* The GM tells you that an unstoppable evil will destroy the world if the PCs don't achieve their quest, and the PCs know that they have no chance in hell of overcoming the opposition.
* The GM insists that he's going to run an "evil campaign" "just for fun", and all PCs must play evil characters. They are then punished every time they do something naughty (let alone "evil"!), relentlessly hounded by other beings far more powerful than they are, and given extremely difficult tasks that can only be overcome by complete co-operation, sympathy and perhaps even self-sacrifice on the part of the PCs.
* The GM tells you that an unstoppable evil will destroy the world if the PCs don't achieve their quest, and the PCs know that they have no chance in hell of overcoming the opposition.
* The GM insists that he's going to run an "evil campaign" "just for fun", and all PCs must play evil characters. They are then punished every time they do something naughty (let alone "evil"!), relentlessly hounded by other beings far more powerful than they are, and given extremely difficult tasks that can only be overcome by complete co-operation, sympathy and perhaps even self-sacrifice on the part of the PCs.